1. Field of Invention
The invention generally relates to optical communication receivers. The invention more particularly relates to optically pre-amplified receiver nodes.
2. Description of Related Art
In conventional long-haul optical communications applications, the loss between the laser transmitter and the receiver is typically fixed or otherwise substantially invariant. Therefore, a gain block with fixed optical gain serves the purpose of ensuring that the receiver will receive a signal within the receiver""s dynamic range.
In some applications such as metropolitan optical ring networks, however, the loss between the laser transmitter and the receiver often changes due to changes in the span loss or due to channel upgrades. During channel upgrades, extra OADMs (optical add drop multiplexers) are added into the optical path of existing channels, therefore the loss between the transmitter and the receiver changes.
Furthermore, a complete fiber cut, fiber disconnect or other major fault in either a long haul or metro application can cause a loss of signal. As recognized by the inventors, the restoration of the optical signal following a loss of signal event may damage the receiver and/or cause bit errors.
Hence, in these applications a smart pre-amplified receiver is needed that will adapt to changing conditions such as those outlined above.
The invention includes an apparatus for optically preamplifying a signal being input to a receiving device, comprising: an optical amplifier optically coupled to an input port of the receiving device, the optical amplifier optically amplifying an input signal and outputting the amplified signal to the receiving device; a controller operatively connected to the receiving device, the controller receiving power measurements from the receiving device indicative of the amplified signal""s optical power; and a pump optically coupled to said optical amplifier, the pump injecting pumping light into the optical amplifier to provide the optical amplification of the input signal; the controller commanding a pump power level output by the pump to perform gain control according to the power measurements received from the receiving device; and the controller commanding the pump power level output by the pump such that the optical amplifier turns off gain control when the power measurements received from the receiving device are inside a first window of received power values.
Furthermore, the controller may command the pump power level output by the pump such that the optical amplifier turns on gain control when the power measurements received from the receiving device are outside a second window of received power values.
Still further, the controller may change a rate of commanded pump power level changes according to how much a current received power level differs from a target received power level.
Alternatively, the controller may change the rate of commanded pump power level changes such that the rate is decreased as the magnitude of the difference between the current received power level and the target received power level decreases.
In another alternative, the controller may change the rate of commanded pump power level changes to a first, second and third value when the magnitude of the difference between the current received power level and the target received power is greater than a first, second and third threshold, respectively.
In general, the controller may also limit a rate of change of pump power levels.
Also, the controller may place a limit on the commanded pump power level such that the controller only permits said pump to amplify the input signal up to the limit and thereby prevents damage to the receiving device.
The invention also includes a method of optically preamplifying a signal being input to a receiving device with an optical amplifier optically communicating with an input of the receiving device, comprising: receiving power measurements indicative of the amplified signal""s optical power; commanding a pump power level of a pump optically coupled to the optical amplifier, the pump injecting pumping light into the optical amplifier to provide the optical amplification of the input signal; controlling said commanding step to perform gain control according to the power measurements received by said receiving step; and said controlling step controlling said commanding step to command the pump power level output by the pump such that the optical amplifier turns off the gain control when the power measurements received from said receiving step are inside a first window of received power values.
The controlling step may control the commanding step to command the pump power level output by the pump such that the optical amplifier turns on the automatic gain control when the power measurements received from said receiving step are outside a second window of received power values.
The invention may also change a rate of commanded pump power level changes according to how much a current received power level differs from a target received power level.
Also, the changing step may change the rate of commanded pump power level changes such that the rate is decreased as the magnitude of the difference between the current received power level and the target received power level decreases.
In addition, the changing step may change the rate of commanded pump power level changes to a first, second and third value when the magnitude of the difference between the current received power level and the target received power is greater than a first, second and third threshold, respectively.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.